Earthmoving machines (e.g., track type tractors and/or motor graders commercially available from Caterpillar, Inc.) having an implement such as a bulldozer blade, which is used on a worksite in order to alter a landscape of a section of land. The blade may be controlled by an operator of the machine or control system to perform work on the worksite. For example, the operator may move a lever that controls the movement of the implement through hydraulic mechanisms. Specifically, movement of the lever translates into an electrical signal supplied to the hydraulic mechanisms. The electrical signal causes the hydraulic mechanisms to move, thereby transferring pressure within a cylinder of the hydraulic mechanism. Because the hydraulic mechanisms are coupled to the implement, the transfer of pressure within the cylinder causes the blade to move in a manner consistent with the movement of the lever by the operator.
The electrical signals can be modified based on control gain information, which determines the response of the hydraulic mechanism to lever movement. If the control gain parameters correspond to high control gains, the hydraulic mechanism responds rapidly, but with less stability, to move the cylinder to the desired position. If the control gain parameters are associated with low control gains, however, the electrical signal moves the cylinder at a slower rate, but in a more stable fashion (i.e., reduced overshoot and settling time).
Typically, control gains include a proportional control gain (Kp) and a derivative control gain (Kd), which are calculated by a proportional-plus-derivative controller to generate an electrical signal referred to as a control effect lift command (CELC) signal. In particular, the CELC signal is calculated by the proportional-plus-derivative controller circuit in accordance with the following formula:CELC=Kp*ebh+Kd*d(ebh)/dt 
In the above equation, Kp is the proportional control gain, ebh is an error in the blade height between a target height and an actual height, Kd is the derivative control gain, and d(ebh)/dt is an instantaneous rate of change of the error in blade height between a target height and an actual height.
Generally, the control gains (Kp and Kd) are manually tuned by an operator depending upon conditions of the worksite. For example, factors such as implement or blade loads, material properties, and machine travel speed determine the level of precision for which the blade is controlled, and thus, the control gains associated with such blade control. Accordingly, for a given combination of such factors, particular control gains are selected. If other factors are present, however, the control gains must be manually changed for a desired hydraulic mechanism response.
The weight of the material in the implement and the forces acting on the implement as a result of the material properties result in variation in the hydraulic control system “damping.” Specifically, if the machine is operated in a material such as loose rock or sand, the control gain will be set to be within a range that will allow stable control of the blade load. If the control gains are set too high, the control system may not be able to accurately control the contents of the blade, thereby causing spillage, unwanted gouges in the worksite, and/or injury to others. Other material properties may require control gains with different values in order to optimize performance of the machine. For example, if the worksite includes a layered material such as shale, excessive force may be necessary to cut through such material. Thus, control gains required for cutting layered materials may be higher than for materials requiring low gain, such as loose rock or sand. Similarly, if the machines are to be operated at high speeds, high control gains are desired compared to operating at low speeds, because the control system may require more control of the contents of the blade. In existing systems, either the range of materials is restricted or manual adjustment is required.
While the manual adjustment of the control gains does allow for some range in working conditions as explained in the factors above, currently, machines are limited to the worksite condition for which the control gains are manually tuned. Accordingly, operators are required to be experienced and skilled in knowing when and what adjustments are needed based upon the factors described above.
U.S. Pat. No. 5,560,431 to Stratton et al. discloses an automatic adjustment of control gains to account for changing ground profiles. The system of Stratton et al. measures certain parameters (as explained below) so that a maximum productivity can be achieved in moving materials from a worksite or altering the geography of a worksite. The system of Stratton et al. detects a true ground speed of an earthmoving machine (e.g., a tractor). The system also senses an angular rate of the machine and senses the position of a lift actuator included with an earthmoving implement (e.g., a tractor blade). In addition, an amount of slip rate is determined, in which the tractor tracks do not adequately engage with the ground as the operator attempts to move the machine. The system also determines a position of the implement as a function of the slip rate value, the angular rate, and the position of the lift actuator, as well as adjusting control gains based on these parameters in order to achieve maximum productivity. Operating the machine to maximize productivity may only concern physical movement of material without regard to the finished appearance of the work surface. Thus, in order to maximize productivity (i.e., set the control gains to a high enough level to ensure that as much material can be moved as possible), the control gains are adjusted based upon many parameters, such as the ground speed, the slip rate, the angular rate, and the position of the lift actuator. However, Stratton et al. does not take into account automatic adjustments of the control gains for “finished dozing,” in which operators of the earthmoving machines seek to maintain a level profile of the worksite or a particular appearance of the work surface in accordance with a predetermined plan. Thus, as opposed to maximum productivity, control gains for finished dozing may be lower to ensure a less aggressive response by the proportional-derivative controller. Using Stratton et al. for “finished dozing” operations may not be suitable, because adjusting the control gains for a more aggressive response by the proportional-derivative controller may cause spillage, and unwanted gouges in the worksite.
The disclosed system is directed at overcoming one or more of the shortcomings in the existing technology.